For the purposes of this study a residential water treatment (RWT) system is defined as:

Point-of-entry (POE) systems: Point-of-entry or whole house systems treat all the water entering the home.

Point-of-use counter top (CT) systems: Counter top systems can either be placed on the kitchen counter or can be wall mounted (typically in Asia).

Point-of-use under-the-sink (UTS) systems: The UTS systems are usually placed under the kitchen sink and do not clutter the kitchen counter.

Point-of-use faucet mount (FM) systems: FM are small filters that go directly on the end of a faucet and are relatively easy to install. FM systems and have low capacities and low flow rates as compared to pitchers and other types of water treatment systems.

Pitcher systems: These systems are also knows as jug filters in certain parts of the world. Water is filtered by gravity through a filter cartridge, mostly made up of carbon. Pitchers and faucet mount systems are cheap residential water treatment systems available to consumers.